Zirconium lamp-filament.



CHARLES A. HANSEN, OF SCHENECTADY, NEW YORK, ASSIGNOR T GENERAL ELECTRIC COMPANY, A CORPORATION OF NEW YORK.

. ZIRCONIUM LAMP-FILA MENT.

menses.

Specification of Letters Patent.

Patented. an. 2c, 1914..

No Drawing. Application filed February 19, 1908, Serial No. 416,681. Renewed June 8, 1910. Serial No.

' The element zirconium has from time to time been proposed as one of the components of lamp filaments of complex composition containing such materials as carbon,

, zirconia, and zirconium carbid, but its use in this way involves many practical difiiculties,

and is by no means general in the art of lamp making.

My present invention relates to the production of pure zirconium filaments, embodies some features very advantageous to commercial manufacture. According to my invention, zirconium oxalate, mixed with carbon or other suitable reducing agent, is squirmd or otherwise formed into threads, and is then subjected to a heat treatment yielding a filament of pure zirconium. I

Zirconium oxalate can be prepared by precipitation of hot zirconium nitrate solution with ammonium oxalate. The precipitate is gelatinous innature, resembling starch paste in consistency, and having a smooth even texture. By using ordinary care during the manufacture, the zirconium oxalate can be made exceedingly pure.

In making up a mixture of zirconium oxalate and carbon, I use such av quantity of carbon as is theoretically necessary to combine with the residual oxygen of the oxalate, thus completely reducing the zirconium compounds without leaving any carbon in the filament. The carbon used for this purpose should be in a finely divided condition, such as lamp black or air blown graphite, and can with advantage be given a preliminary heat treatment in atvacuum to remove gases and volatile impurities.

It should be noted that the squirting mixture just described is held together and rendered tenacious by the zirconium oxalate. The mixture is therefore clearly distinguishable from the squirting mixtures in which a compound of refractory metal is held together by a pitch or syrup. This feature is of particular importance as hereinafter set forth in some detail. Q

' When the mixture of carbon and zirconlum oxalate 1s squirted through adie it comes out as a soft, pliable thread, suitable for winding on forms, or otherwise shaping, as desired. After squirting, the threads or raw filaments are subjectedtoheat treatment to produce the necessary reduction and to densify the zirconium.

The heat treatment may be applied simul taneously to entire bundles of raw filaments,

thus obviating the necessity for individual hand treatment, so common in metal filament manufacture. As a furnace for use in this heat treatment, I may use the one described in United States Patent to Arsem, No. 7 85,535, March 21st 1905, though I prefer to use in "place of the graphite heater there shown, a heater consisting entirely of tungsten. This insures an atmosphere free from carbon. Such a tungsten furnace can be run to temperatures high enough to completelyshrink or sinter the zirconium resulting from the reduction, but, if desired, the heat treatment may be stopped somewhat short of complete shrinkage, thus permitting completion and shaping of the filament in treating bottles or in t-helamp bulbs themselves' The heat treatment in the furnace is not a delicate operation for the reason that with up in differentways at different temperatures, thus rendering uncertain, the quantity of carbon left behind to serve as a reducing agent. In some filament processes a carbonaceous binder cannot be dispensed with, but such is not the casein my presentvprocess wherein the gelatinous zirconium oxalate is made to serve both as a binder and as the reducible compound.

What I claim as new, and desire to secure by Letters Patent of the United States, is,

1. The method which consists in mixing zirconium oxalate with finely divided carbon, shaping the mixture into threads and heating said threads to produce refractory filaments consisting essentially of zirconium.

-2. The method whichconsists in mixing gelatinous zirconium oxalate with'a finely powdered reducing agent, shaping the mixture into threads and heating to oxidize said reducing agent.

3. The method which .consistsin mixing zirconium oxalate with finely divided carbon; shaping the mixture into threads and subsequently heating to oxidize the carbon,

the carbonand oxalate of the mixture being in such proportion that pure zirconium will result from the heat treatment.

4:. The method which consists in mixing powdered carbon with gelatinous zirconium oxalate, shaping the mixture into threads, and then heating said threads in an inert and rarefied atmosphere to produce coherent conductors of pure zirconium. 

